Demand for lower freight transportation cost is driving up the average freight car weight around the world. To carry heavier weight, the freight cars must be equipped with strong bearings capable of carrying both axial and radial loads.
Tapered roller bearings efficiently carry both axial and radial loads. A tapered roller bearing includes one or more rows of tapered rollers. Each row encircles the rotation axis of the bearing. Each tapered roller has the shape of a truncated cone. This geometry allows the tapered roller bearing to support axial loads (loads parallel to the rotation axis of the bearing). A popular choice for freight cars is the double-row tapered roller bearing which has two rows of tapered rollers. The two rows are tapered in opposite directions to locate the shaft, or journal, in both directions along the rotation axis.
Tapered roller bearings, as well as other types of roller bearings, operate with a lubricant within the bearing to reduce friction between the rollers and the raceways on which the rollers roll. To contain the lubricant within the bearing and to prevent water, dirt, and other contaminants from entering the bearing, the bearing is sealed. The seal may be a contact seal that forms a physical barrier between the inside of the bearing and the external environment. Common contact seals include a rubber ring that seals a gap between a rotating and non-rotating portion of the roller bearing.